Currently, 15% of couples present difficulties to conceive and one in seven men present alteration of sperm quality (Krausz 2011). The semen is constituted of a non-cellular phase, the seminal plasma, a complex fluid composed of prostatic and seminal vesicle secretions and a cellular phase containing spermatozoa. To evaluate the quality of the semen, a descriptive analysis is often performed. Essential sperm parameters are evaluated including the sperm concentration, the motility and the morphology of spermatozoa. The lower reference limits of these parameters are given according to the WHO criteria (2010). Motility, morphology and sperm count are considered as markers of fertility and used to predict pregnancy success (Aitken 2006). Despite having apparently normal sperm parameters, the origin of men infertility remains unknown for 50% of individuals classified as having a normozoospermia (Krausz 2011). Thus, fertilization failure are yet observed and remains ill-defined (Krausz 2011). With this in mind, descriptive analyses of the semen show limits to predict fertility and new tools are certainly needed to understand sperm physiology and define a new approach to identify the origins of men fertilization failure as well as to help couples orientation to current assisted reproduction technologies (ART).
Spermatozoa should be considered to define the fertility index. Spermatozoa are highly differentiated cells. During spermatogenesis, they progressively lose their cellular organelles with the cytoplasmic droplet and became motile and able to fertilize during their maturation in the epididymis and in female genital tractus. Hereby, there is no or weak protein synthesis in a mature spermatozoa. However, spermatozoa cell and its environment (epididymis, male and female genital tractus) interact and might consequently modifying the spermatozoa proteome (Plessis et al. 2011). Currently, recent advances in proteomic technology have produced valuable tools for studying sperm proteins. Proteins studied and proposed as potential fertility marker are mostly revealed through their fertility functions. First, due to crucial role of the sperm nucleus, the ratio protamine 1 (P1)/protamine 2 (P2) is widely studied and P1/P2 ratio is correlated with fertilization ability (Aoki et al. 2006; Oliva 2006; de Mateo et al. 2007; de Mateo et al. 2009). De Mateo and collaborators demonstrated a negative correlation between prohibitin expression, a mitochondrial protein implied in sperm motility (Wang et al. 2012), and level of P1/P2 ratio (de Mateo et al. 2007). Acrosomal vesicle is required for spermatozoa penetration of the oocyte zona pellucida and acrosin expression is used as a marker of its integrity (Zahn et al. 2002); (Liu et al. 2008). Chaudhury et al. studied proacrosin/acrosin expression in men with normal sperm parameters but unexplained infertility. Proacrosin/acrosin system seems to be disturb in men with normal sperm parameters but unexplained infertility and proposed this protein as a marker (Chaudhury et al. 2005). More recently, Blomberg Jensen and collaborators (Blomberg Jensen et al. 2012), proposed for the first time vitamin D metabolizing enzyme CYP24A1 expressed in the annulus of spermatozoa as a novel marker of semen quality. Sperm membrane is a fundamental actor in fertility and its composition can be disturb by several factors such as oxygen reactive species of thus induce the dysfunction of spermatozoa fertility (Glander et al. 2002; Aitken 2006; Cocuzza et al. 2007; Bresler et al. 2011; Aitken 2011). Yet, many alterations of sperm proteome may contribute to male infertility and those factors remain ill-defined.